DEVELOPMENT
Not Applicable
1. Field of the Invention
This application pertains to safety means responsive to an obstruction to closure of a movable closure element, and is particularly applicable to anti-trap window sensing for use in automobiles.
2. Background Information
A safety problem associated with powered panel closures is that a person, animal, or inanimate object may get in the way of the moving panel. This can obstruct the motion of the panel, but more importantly, can cause severe injury. Of particular interest is the operation of electrically powered automobile windows and the provision of an effective means to limit and reverse window travel when a human body part is sensed near the top of the window frame upon closure.
An objective of the invention is to prevent the pinching or trapping of a human body part or foreign object in a window, door, sunroof, hood or trunk lid, or other closure part of a transport vehicle such as a car, van, train, bus, truck, or other conveyance. In general, the invention attains this goal by capacitively sensing the human body part, either before contact with a sensing electrode or plate, or at the time of contact with the plate. The sensing electrode may be a metal strip or wire, which can be embedded in a plastic or rubber molding strip, placed behind a piece of fascia or other trim part, or may simply be a metal element on top of the trim parts. Sensing electrodes of this sort can be prepared from conductive ink, made of adhesive backed metal foil, formed from a metal mesh strip, or simply be a wire or serpentine-laid wire.
The preferred capacitive sensing technology employed in the present invention is the xe2x80x9ccharge transferxe2x80x9d approach developed by the inventor and taught in his U.S. Pat. No. 5,730,165, the disclosure of which is herein incorporated by reference. This form of capacitive proximity sensing uses switching elements to transfer electric charge to and from the sensing plate. Charge cancellation features of this approach allow for a very wide dynamic range and great stability. Although charge transfer is the preferred approach for the invention herein disclosed, this technology is not essential to make such a system operate, and other capacitive techniques known in the art may be used.
Another object of the invention is provide a panel closure sensor that is immune to the effects of moisture and humidity, which are known to seriously affect the performance of many capacitive sensors when water contacts or is capacitively coupled to their sensing electrodes. As described in the inventor""s U.S. Pat. No. 5,730,165, one of the features of the charge transfer sensing approach is a xe2x80x98short pulsexe2x80x99 mode which is notable for its moisture suppression attributes. Thus, a sensor of the invention that comprises a sensing electrode built into or located behind an elastomeric automotive window frame channel is not affected by the presence of water condensed on the window or on the elastomeric channel.
Yet another object of the invention is to provide a capacitive sensor for a panel closure control system that is not affected by either rapidly or slowly changing environmental conditions. A preferred sensor of the invention comprises xe2x80x98smart algorithmsxe2x80x99 that adapt dynamically to the environment. This feature allows the sensor to ignore changes in ambient temperature, changes in window mechanics and dynamics, and the build-up of dirt and underlying changes in material properties over long periods of time. In a preferred embodiment, this involves two mechanism of adaptation: A) A full recalibration of the signal reference point internal within the sensor, so that the baseline signal is known. B) A mechanism for compensation for slow change in signals over time, i.e., signal drift, whereby the baseline internal reference level is altered more slowly than in the case of full recalibration to accommodate slow changes in signal due to humidity or changing mechanical parameters.
Yet another object of the invention is to provide sensing and control apparatus in which the sensitivity to an obstruction (e.g., a person""s hand) is not affected by whatever proximity signals are measured from the panel that is being closed. In a preferred embodiment of the invention the sensor records the amount of signal generated by the closure part during a normal and unobstructed closure, correlates that signal with the degree of closure; and creates a table of values of expected signal vs. closure part extension, which is later used to create a xe2x80x98subtraction signalxe2x80x99 to remove the effects of the normal closure part from a signal that may also comprise component due to an obstruction. That is, the system subsequently controls the motor to move the panel from the open to the closed state and compares, at each of the plurality of position values sensed by suitable position sensing means, the respective stored capacitance value with a currently measured capacitance value; and stops the motion of the panel if the stored and the currently measured capacitance values differ by more than a predetermined threshold amount.
Conversely, it is a related object of the invention to provide sensing and control apparatus in which small changes in the sensing plate""s environment (e.g., change in dimension of a rubber window channel that enrobes a sensing wire) do not cause false alarms in which the travel of panel is stopped short of closure even though no obstruction is present This may be done by desensitizing the system as the panel nears its closed state (e.g., during the last one or two centimeters of the travel of a dosing window). In the case of a system using an expected signal table, as described in the preceding paragraph, one can use two threshold values. The larger of the two threshold values is used when the panel is within some predetermined distance of its closed state. The smaller of the two threshold values is applied during the rest of the travel distance between the open and the closed states.
Yet a further object of the invention is to provide a control system that does not respond to an obstruction when a controlled panel is in either of its opened or closed states. For example, an automotive window control system should not open a fully dosed window if a passenger accidentally or intentionally places his or her hand adjacent a top of the window frame. Nor should such a system attempt to open a window that was already in its fully opened state. Thus, a preferred system of the invention comprises at least one end-of -travel sensor or other means of sensing when a controlled panel is in its opened or closed positions. The sensing elements used for this function may be different from those employed for sensing obstruction during periods in which the panel is traveling between the two limiting positions.
A control system of the invention that is responsive to an obstruction to a panel closure may involve the use of other sensors in addition to a capacitive anti-trap sensor. Generally speaking, a system of this sort uses a motor to move a panel from an open state in which a leading edge of a panel is distal from a frame portion to a closed state in which the leading edge is adjacent the portion of the frame. The system comprises a controller that controls the motor responsive to various sensor and switch inputs, and has end-of-travel sensors for sensing when the panel is in the opened or the closed state. The control system of the invention comprises a capacitive obstruction sensing means comprising a sensing plate near or within the panel frame, a source of DC current for charging the plate; a voltage pulse source; and a discharging switch having an open state and a closed state, the discharging switch moving from its open to its dosed state responsive to the voltage pulse, the discharging switch connecting the plate to a charge measuring means when in the dosed state, the discharging switch otherwise not connecting the plate to the charge measuring means. In preferred embodiments the capacitive sensor further comprises both a charging and a discharging switch.
In the particular application of providing an anti-trap sensor for an automobile window, one must provide for satisfactory operation even when the window and frame are wet In these cases the capacitive sensing plate is electrically coupled to an electrical ground by a shunting conductor (i.e., the water) substantially conducting electrical current pulses having durations greater than a first predetermined value, but not conducting current pulses having durations less than a second predetermined value. The invention uses short duration voltage pulses for capacitive measurement in order to allow the anti-trap sensor to ignore the effects of water films or of high humidity.
Although it is believed that the foregoing recital of features and advantages may be of use to one who is skilled in the art and who wishes to learn how to practice the invention, it will be recognized that the foregoing recital is not intended to list all of the features and advantages. Moreover, it may be noted that various embodiments of the invention may provide various combinations of the hereinbefore recited features and advantages of the invention, and that less than all of the recited features and advantages may be provided by some embodiments.